Two gastric antrum biopsies of each of 92 consecutive patients undergoing gastroendoscopy were studied. The first biopsy was cultured for Helicobacter (Campylobacter) pylori. The second specimen was fixed and processed for histopathological analysis. The bacteria were isolated from 34 (81%) of 42 patients with nonspecific chronic gastritis, 19 (90%) of 21 cases of duodenal or gastric peptic ulcer, and from 3 (23%) of 13 normal patients. The overall frequency of isolation was 62 (67%) of the 92 cases.